This invention relates to a brush seal for sealing between two components, e.g., a stationary component and a fixed component and, more particularly, relates to a brush seal whose position can be changed in two perpendicular directions relative to the components, e.g., radial and axial directions relative to fixed and rotating components.
In turbomachinery, brush seals are typically installed in a fixed position on a stationary component. The turbomachinery comprises many individual components, such as wheels, buckets, nozzles, diaphragms, casings, bearings and the like, each with its own manufacturing tolerances. As a result, when clearances between stationary and rotating components are measured at final assembly, different and relatively large variations in clearances can be expected due to the accumulation of the component manufacturing tolerances. During operation of the turbomachinery, the clearances between the components may also change due to differences in thermal expansion and the effects of rotation. Brush seals must be designed to accommodate these variations in clearances and to prevent a xe2x80x9chard rubxe2x80x9d condition wherein the brush seal backing plate contacts the rotating component. In applications in turbomachinery where the space allotted for the brush seal is very limited, it becomes very difficult, if not impossible, to accommodate all of the manufacturing tolerances and provide a sufficient clearance margin to avoid a hard rub with the current brush seal designs.
Brush seals are currently mounted within a stationary component, typically a diaphragm, or nested within a labyrinth seal, using a T-shaped or L-shaped slot to establish the axial and radial position of the brush seal. Typically, the seal is repositionable only to the extent the position of the component carrying the brush seal, e.g., a diaphragm, is likewise repositionable. The position of the brush seal with respect to the carrier component is conventionally not repositionable. Accordingly, there is a need for a brush seal assembly which enables the position of the brush seal to be changed relative to its carrier component.
In a preferred embodiment of the invention, a brush seal assembly is provided wherein the position of the brush seal can be changed relative to the carrier component in at least one direction and preferably in two directions generally perpendicular to one another. The brush seal typically includes a pair of backing plates and elongated bristles disposed between the backing plates and terminating in bristle tips spaced from margins of the backing plates for engagement with the rotating component. It is desirable to be able to reposition the brush seal in both axial and radial directions relative to the rotating component. To accomplish this, an annular or arcuately segmented brush seal is provided with a mounting member receivable within an axially opening slot or groove formed on the stationary component. By forming the slot or groove to a length exceeding the length of the mounting member and with the mounting member extending normal to the plane of the brush seal, the brush seal may be repositioned axially into the desired position. To change the position of the brush seal in a radial direction relative to the stationary and rotating member, shims are deployed on opposite sides of the mounting member and between the walls of the slot or groove. By varying the thicknesses of the shims between the brush seal and the slot or groove, the radial location of the brush seal is changed relative to the shaft. To fix the brush seal in the new position, two or more pins or screws may be used to secure the brush seal to the stationary component. In this embodiment, as well as other embodiments hereof, the seal may be repositioned in this manner as part of an original equipment manufacture or during a retrofit of the seal into the turbomachinery. Thus the turbomachinery may be delivered to an installation site with the stationary component having pre-drilled, undersized holes and the brush seal provided without pre-drilled holes. The final location of the holes on the brush seal is determined based on measurements at assembly. Pins or screws also provide an anti-rotation feature which prevents the brush seal from being displaced circumferentially relative to the fixed component.
In another preferred embodiment of the invention, set screws are employed to change the position of the mounting member relative to the stationary component in a radial direction. Once the desired radial position is obtained, the screws can be staked to the brush seal to prevent further rotation, thus fixing the position of the brush seal. The axial position of the brush seal is repositioned by inserting a laminated shim pack into the slot or groove of the fixed component. This laminated shim pack may be formed of individual foils, for example, 0.004 inches thick, joined by an adhesive. By removing layers of the foil from the shim pack, the axial position of the brush seal relative to the fixed component can be accurately determined.
Brush seals are typically applied in turbomachinery in arcuate segments whereby a plurality of segments form a complete annulus about the rotating component. In a further preferred embodiment of the invention, each segment is provided with an eccentric cam rotatable about an axis. The segment includes a cam follower positioned so that rotation of the cam causes the segment to be displaced in a radial direction, thereby repositioning the brush seal relative to the two components. At least a pair of eccentric cams are utilized for repositioning each segment.
In a still further preferred embodiment of the invention, the brush seal radial and axial positions are set by shims. The brush seal segment is secured to the stationary or fixed component by radial socket head cap screws and retaining pins. The brush seal segment has slots machined to accept the socket head cap screws. Once the radial and axial position of the seal has been set, the cap screws can be tightened to secure the assembly. By tack-welding the screw heads to the brush seal, loosening of the screws is prevented. Additional strength to the assembly is provided by installing retaining pins through the mounting arm and fixed component.
In another preferred embodiment of the invention, a repositionable seal assembly is provided for sealing between first and second components. This assembly comprises a brush seal for securement to the first component and having a plurality of bristles disposed between a pair of backing plates, the bristles arranged in a common plane and projecting from between the plates to terminate in bristle tips for sealing engagement with the second component, a mounting member carrying the brush seal for securing the brush seal to the first component, at least one shim cooperable between the first component and the mounting member for repositioning the brush seal relative to the first component in one of first and second directions, respectively generally perpendicular and parallel to the plane, and at least one fastener for securing the brush seal to the first component in a new position.
In a further preferred embodiment of the invention, a seal assembly for a turbine comprises a first, generally annular component fixed against rotation, a second component rotatable about an axis, and a seal assembly between the first and second components including a brush seal carried by one of the first and second components. The brush seal includes a plurality of bristles carried by at least one mounting plate and projecting from the mounting plate to terminate in bristle tips for sealing engagement with another of the first and second components, and a mounting member for mounting the brush seal to one component. The seal assembly further includes at least one shim cooperable between one component and the mounting member to reposition the brush seal relative to one component in one of first and second directions, respectively generally perpendicular and parallel to the axis, and at least one fastener securing the brush seal and one component to one another in the new position.